1. Field of the Invention
The invention relates to reconstituted tobacco and methods for its production. In general, the production and processing of tobacco products includes the steps of aging, blending, cutting, drying, cooling, screening, shaping and packaging which generate considerable amounts of tobacco fines and dust. Furthermore, tobacco midribs, called stems, are not considered useful directly in producing such products and are separated from the tobacco leaf. Rather than discard these fines, powder and stems, it has been customary to form them into a sheet material resembling leaf tobacco and commonly referred to as reconstituted tobacco. There are currently three processes used commercially to form reconstituted tobacco: the two-step paper process, the single-step paper process, and the casting process. Each of these processes involves forming a liquid slurry or paste, and they all have in common high drying energy requirements. In addition, the paper making processes have high capital costs and commonly result in losses of material to the sewer. The casting process, on the other hand, while having a relatively low capital cost, is still essentially a wet process and results in marginal physical properties as well as requiring the use of large amounts of gum binder. The present invention is directed to an improved method for forming reconstituted tobacco that avoids these drawbacks and to the resulting reconstituted tobacco product.
2. Description of the Prior Art
As mentioned above, one conventional method for manufacturing reconstituted tobacco involves standard papermaking techniques. In this case, prior to refining, the tobacco is usually soaked in water to extract the water soluble portion. The aqueous extract is put aside and after the fibrous tobacco remainder is refined and formed by conventional papermaking techniques, the extract is reintroduced into the web and final drying takes place. For example, U.S. Pat. No. 4,182,349 to Selke dated January 8, 1980 describes this process and improvements thereto relating to the refining step. A second process in use is to dry grind or mill tobacco leaves, stocks or stems, add the grindings to an aqueous or other liquid carrier and, after addition of a binder, cast the moist mass onto a stainless steel belt or other carrier. The web is then dried to the desired moisture content. U.S. Pat. No. 3,429,316 to Hess, dated February 25, 1969 describes improvements to the casting process including particular additive materials and also discusses similar steps for making reconstituted tobacco. Variations of the casting process are also taught in U.S. Pat. Nos. 2,734,510 and 2,734,513, both to Hungerford, et al. and dated Feb. 14, 1956 and incorporating the use of a film forming binder matrix. Known processes have in common the use of water or another liquid vehicle for web formation. While the amount of such a liquid vehicle varies considerably, in all cases it must be at least sufficient to form a doughy mass, and usually is in amounts sufficient to at least form a slurry. Further, to achieve satisfactory properties, it is frequently taught as necessary to extract tobacco liquor and return it to the formed sheet. In such processes where large volumes of water are utilized, environmental concerns necessitate steps to assure that any undesirable impurities are removed from process water prior to returning it to streams or local water systems. Other problems relating to the use of water vehicles and processes for reconstituting tobacco are described in U.S Pat. No. 3,310,057 to Savage, Midland and Aldrich dated March 21, 1967.
It is also known, generally, to form paper webs by dry forming processes. Since Fourdrinier paper machines historically have required large volumes of water necessitating further processing and disposal, much effort has been directed to dry forming of paper. Representative examples of such processes are described in U.S. Pat. No. 3,575,749 to Kroyer dated April 20, 1971 and U.S Pat. No. 3,669,778 to Rasmussen dated June 13, 1972. Such dry forming processes for paper manufacture have not, however, achieved widespread success due to a failure to achieve desired strength properties on an economic basis. Moreover the investigation of such processes has heretofore been limited to woodpulp fibers due to the high degree of fiberization essential to obtain fiber separation and a uniform product.
In summary, the available art demonstrates the need for improved techniques to form reconstituted tobacco and products that would improve the economies of such materials while maintaining or improving desired properties.